Flapper valves and other types of downhole valves can be damaged if a tool string is allowed to pass through them when they are in the closed condition. For example, the tool string run through the valve can damage the valve's flapper when closed. Also, the tool string even if capable of passing through the closed flapper may not be allowed to pass back up through the flapper so that the tool sting becomes trapped by the valve.
From the surface, operators do not always know if the flapper in these type of valves is open or not. Typically, operators must run a wireline drift tool through the valve to determine if the flapper is open or closed. If the flapper is open, then the drift tool is able to pass through. If the flapper is closed, the drift tool will stick through the flapper which then activates an artificial hold open sleeve to allow for the drift tool to be retrieved. Another way operators can determine whether a flapper is open or closed involves running a camera downhole and feeding back images to the surface.
Sometimes, a downhole valve may have dogs that engage a specifically designed stringer used to open and close the valve. For example, Weatherford's completion isolation valve (CIV) is a ball type valve actuated by a stinger. Dogs in the CIV engage the stinger and allow the stinger to move internal components to open and close the valve's ball seal. In this instance, these dogs move with the internal components of the valve that operate the ball seal. Therefore, these dogs are directly used to operate the valve by engaging the stinger and not to passively prevent a generic type of tool from being passed through the valve when closed.
What is needed is a way to reliably and easily prevent potential damage to a downhole valve by a generic tool string and to prevent entrapment of the tool string in the valve by passively preventing mechanical passage of the tool string in the valve when closed.